d3dx9/tests: Fix volume test boxes.
This test seems to be testing different filters when creating volumes, and nothing indicates it's intentionally testing volume creation from out-of-bound srcboxes.
The pixels array is 16x4 bytes, pixel format D3DFMT_A8R8G8B8 is 4 bpp, so pixels have 16 pixels in total. The boxes have 2 slices, with a slice pitch of 32 bytes, that's 8 pixel/slice. The original widthheight is 66 which is thus beyond these bounds. This commit changed it to 4*2 so the rowpitch of 16 bytes is perserved.